The specific objective of this study is to determine if infants with hypoplastic left-heart syndrome have altered resting myocardial perfusion and coronary artery reserve compared to other postoperative infants with congenital cardiac defects. The control group will consist of surgically repaired defects not thought of potentially restricting myocardial perfusion. Quantitation of coronary artery reserve will be rendered by Positron Emission Tomography (PET) before and after adenosine infusion.